Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D498/00—Heterocyclic compounds containing in the condensed system at least one hetero ring having nitrogen and oxygen atoms as the only ring hetero atoms
  • C07D498/12—Heterocyclic compounds containing in the condensed system at least one hetero ring having nitrogen and oxygen atoms as the only ring hetero atoms in which the condensed system contains three hetero rings
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P25/00—Drugs for disorders of the nervous system
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P25/00—Drugs for disorders of the nervous system
  • A61P25/18—Antipsychotics, i.e. neuroleptics; Drugs for mania or schizophrenia
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P25/00—Drugs for disorders of the nervous system
  • A61P25/24—Antidepressants
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P25/00—Drugs for disorders of the nervous system
  • A61P25/28—Drugs for disorders of the nervous system for treating neurodegenerative disorders of the central nervous system, e.g. nootropic agents, cognition enhancers, drugs for treating Alzheimer's disease or other forms of dementia
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P43/00—Drugs for specific purposes, not provided for in groups A61P1/00-A61P41/00
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D498/00—Heterocyclic compounds containing in the condensed system at least one hetero ring having nitrogen and oxygen atoms as the only ring hetero atoms
  • C07D498/12—Heterocyclic compounds containing in the condensed system at least one hetero ring having nitrogen and oxygen atoms as the only ring hetero atoms in which the condensed system contains three hetero rings
  • C07D498/14—Ortho-condensed systems

Definitions

• This invention relates to the prevention and treatment of cerebral insufficiency, including enhancement of receptor functioning in synapses in brain networks responsible for higher order behaviors.
• the invention relates to methods for the use of the compounds disclosed herein, and to methods for the preparation thereof.
• AMPA/quisqualate receptors mediate a voltage independent fast excitatory postsynaptic current (the fast epsc) whereas NMDA receptors generate a voltage-dependent, slow excitatory current.
• fast epsc a voltage independent fast excitatory postsynaptic current
• NMDA receptors generate a voltage-dependent, slow excitatory current.
• AMPA receptors are not evenly distributed across the brain but instead are largely restricted to telencephalon and cerebellum. These receptors are found in high concentrations in the superficial layers of neocortex, in each of the major synaptic zones of hippocampus, and in the striatal complex, as reported by Monaghan et al., in Brain Research 324:160-164 (1984). Studies in animals and humans indicate that these structures organize complex perceptual-motor processes and provide the substrates for higher-order behaviors. Thus, AMPA receptors mediate transmission in those brain networks responsible for a host of cognitive activities.
• LTP long-term potentiation
• LTP is the substrate of memory.
• compounds that block LTP interfere with memory formation in animals, and certain drugs that disrupt learning in humans antagonize the stabilization of LTP, as reported by del Cerro and Lynch, Neuroscience 49:1-6 (1992).
• a possible prototype for a compound that selectively facilitates the AMPA receptor was disclosed by Ito et al, J. Physiol. 424:533-543 (1990).
• nootropic drug aniracetam N-anisoyl-2-pyrrolidinone increases currents mediated by brain AMPA receptors expressed in Xenopus oocytes without affecting responses by ⁇ - aminobutyric acid (GABA), kainic acid (KA), or NMDA receptors.
• GABA ⁇ - aminobutyric acid
• KA kainic acid
• NMDA receptors NMDA receptors.
• Infusion of aniracetam into slices of hippocampus was also shown to substantially increase the size of fast synaptic potentials without altering resting membrane properties. It has since been confirmed that aniracetam enhances synaptic responses at several sites in hippocampus, and that it has no effect on NMDA-receptor mediated potentials.
• aniracetam has also been found to have an extremely rapid onset and washout, and can be applied repeatedly with no apparent lasting effects; these are valuable traits for behaviorally-relevant drugs.
• the peripheral administration of aniracetam is not likely to influence brain receptors.
• the drug works only at high concentrations ( ⁇ 1.0 mM) and Guenzi and Zanetti, J. Chromatogr. 530:397-406 (1990) report that about 80% of the drug is hydrolyzed to anisoyl-GABA following peripheral administration in humans.
• the metabolite, anisoyl-GABA has been found to have only weak aniracetam-like effects.
• Ampakines are disclosed in International Patent Application Publication No. WO 94/02475 (PCT/US93/06916) (Lynch and Rogers, Regents of the University of California).
• the Ampakines generally are substituted benzamides, are chemically more stable than aniracetam, and show improved bioavailability as judged by experiments performed by Positron Emission Tomography (PET) [see, for example, Staubli et al, in PNAS 91: 11158-11162 (1994)].
• PET Positron Emission Tomography
• Invention compounds are demonstrated in the examples that follow to possess surprising biological activity as evidenced by their ability to increase AMPA receptor function in slices of rat hippocampus, to be substantially more metabolically stable than structurally related Ampakines, and to promote improvement in relevant memory tasks, such as performance in an eight-arm radial maze.
• the compounds of the present invention are acylbenzoxazines having the following formula:
• R 1 and R 2 are either individual monovalent moieties or joined together to form a single divalent moiety.
• R 1 and R 2 are either the same or different and are each either H, CH 2 OR 4 , or OR 4 provided that at least one of R 1 and R 2 is not H, and in which R 4 is either H, C,-C 6 alkyl, C,-C 6 fluoroalkyl, C 7 -C 12 arylalkyl, or C 3 -C 10 heteroarylalkyl.
• R 1 and R 2 together form a group selected from
• R 6 is H, cyano, OH, C,-C 6 alkyl, C,-C 6 fluoroalkyl, C 7 -C 12 arylalkyl, or C 3 -C 10 heteroarylalkyl, C 3 -C 10 heteroarylalkyl, or OR 4 , and R 4 is the same as above;
• R 7 is H, C,-C 6 alkyl, C,-C 6 fluoroalkyl, C 7 -C 12 arylalkyl, or C 3 -C 10 heteroarylalkyl;
• R 3 is H, C,-C 6 alkyl, or C,-C 6 fluoroalkyl;
• Q is a substituted or unsubstituted lower alkylene, cycloalkyl, aryl, arylalkyl, or heteroarylalkyl;
• X and Y are both independently H, or together form a covalent bond or
• alkyl is used herein to include both straight-chain, branched-chain, and cycloalkyl species.
• fluoroalkyl is used herein to include both single and multiple fluorine substitutions, with perfluorinated C,-C 3 moieties being preferred.
• aryl includes both substituted and unsubstituted carbocylic and heterocylic aromatic species, such as phenyl, tolyl, pyridyl, imidazoyl, alkylenedioxyphenyl, etc.
• R 1 and R 2 are individual monovalent moieties
• preferred compounds are those in which one of these two moieties is H and the other is OR 4 where R 4 is either C,-C 6 alkyl or C,-C 3 fluoroalkyl, with R 4 more preferably being either C,-C 3 alkyl or C,-C 2 fluoroalkyl, still more preferably CH(CH 3 ) 2 or CF 3 , and most preferably CH(CH 3 ) 2 .
• R 3 is preferred to be H
• Q is preferred to be lower alkylene
• X and Y together form a covalent bond.
• an effective amount or “therapeutically effective amount” is used throughout the present application to describe an amount or concentration of one or more of the compounds according to the present invention which is used to produce a desired effect or treat a specific condition in a patient or subject.
• Compounds according to the present invention may be used to improve the performance of a patient on sensory-motor problems, to enhance the performance of subjects involving cognitive tasks dependent upon brain networks utilizing AMPA recptors, to improve the strength of memory encoding or to improve brain functioning in subjects with deficiencies in the number of excitatory synapses or AMPA receptors.
• the present compounds may also be used in effective amounts to decrease the time needed for a subject to learn a cognitive, motor or perceptual task, or for decreasing the quantity and/or severity of errors made by a subject in recalling a cognitive, motor or perceptual task.
• the present compounds are also useful for treating human subjects to enhance synaptic response mediated by AMPA receptors.
• the present compounds may be used to treat schizophrenia, schizophreniform behavior or depression in a human patient or subject. In each instance where the present compounds are used, they are used in amounts or concentrations effective for producing a desired effect or for treating a specific condition in a patient.
• patient or “subject” is used throughout the specification to describe an animal, including a human, to whom treatment or use with the compounds or compositions according to the present invention is provided.
• patient or subject refers to that particular animal.
• sensor motor problems is used to describe a problem which arises in a patient or subject from the inability to integrate external information derived from the five known senses in such a way as to direct appropriate physical responses involving movement and action.
• the term "cognitive task” is used to describe an endeavor by a patient or subject which involves thought or knowing.
• the diverse functions of the association cortices of the parietal, temporal and frontal lobes which account for approximately 75% of all human brain tissue, are responsible for much of the information processing that goes on between sensory input and motor output.
• the diverse functions of the association cortices are often referred to as cognition, which literally means the process by which we come to know the world.
• Selectively attending to a particular stimulus, recognizing and identifying these relevant stimulus features and planning and experiencing the response are some of the processes or abilities mediated by the human brain which are related to cognition.
• the term "brain network” is used to describe different anatomical regions of the brain that communicate with one another via the synaptic activity of neuronal cells.
• AMPA receptor refers to an aggregate of proteins found in some membranes, which allows positive ions to cross the membrane in response to the binding of glutamate or AMPA (DL- ⁇ -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid), but not NMD A.
• excitatory synapse is used to describe a cell-cell junction at which release of a chemical messenger by one cell causes depolarization of the external membrane of the other cell.
• An excitatory synapse is used to describe a postsynaptic neuron which has a reversal potential which is more positive than the threshold potential and consequently, in such a synapse, a neurotransmitter increases the probability that an excitatory post synaptic potential will result ( a neuron will fire producing an action potential).
• Reversal potentials and threshold potentials determine postsynaptic excitation and inhibition.
• the reversal potential for a post synaptic potential is more positive than the action potential threshold, the effect of a transmitter is excitatory and produces an excitatory post synaptic potential (“EPSP”) and the firing of an action potential by the neuron.
• the reversal potential for a post synaptic potential is more negative than the action potential threshold, the transmitter is inhibitory and may generate inhibitory post synaptic potentials (IPSP), thus reducing the likelihood that a synapse will fire an action potential.
• the general rule for postsynaptic action is: If the reversal potential is more positive than threshold, excitation results; inhibition occurs if the reversal potential is more negative than threshold. See, for example, Chapter 7, NETTROSCIENCE. edited by Dale Purves, Sinauer Associates, Inc., Sunderland, MA 1997.
• motor task is used to describe an endeavor which is taken by a patient or subject which involves movement or action.
• perceptual task is used to describe an act by a patient or subject of devoting attention to sensory inputs.
• synaptic response is used to describe biophysical reactions in one cell as a consequence of the release of chemical messengers by another cell with which it is in close contact.
• Schizophrenia is used to describe a condition which is a common type of psychosis, characterized by a disorder in the thinking processes, such as delusions and hallucinations, and extensive withdrawal of the individual's interest from other people and the outside world, and the investment of it in his or her own. Schizophrenia is now considered a group of mental disorders rather than a single entity, and distinction is made between reactive and process schizophrenias.
• schizophrenia or schizophreniform embraces all types of schizophrenia, including ambulatory schizophrenia, catatonic schizophrenia, hebephrenic schizophrenia, latent schizophrenia, process schizophrenia, pseudoneurotic schizophrenia, reactive schizophrenia, simple schizophrenia, and related psychotic disorders which are similar to schizophrenia, but which are not necessarily diagnosed as schizophrenia per se.
• Schizophrenia and other psychotic disorders may be diagnosed using guidelines established in, for example, Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM IV) Sections 293.81, 293.82, 295.10, 295.20, 295.30, 295.40, 295.60, 295.70, 295.90, 297.1, 297.3, 298.8.
• DSM IV Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition
• brain function is used to describe the combined tasks of perceiving, integrating, filtering and responding to external stimuli and internal motivational processes.
• the compounds of the present invention can be synthesized in a variety of ways, using conventional synthetic chemistry techniques.
• One method for the preparation of the compounds of the present invention comprises: preparing an ortho hydroxy substituted benzyl amine by contacting a suitably substituted phenol with hydroxymethylphthalimide in an inert solvent with a suitable catalyst such as an aryl or alkylsulfonic acid or other Lewis acid catalyst known to those skilled in the art.
• a suitable catalyst such as an aryl or alkylsulfonic acid or other Lewis acid catalyst known to those skilled in the art.
• the benzylic amine is liberated by treatment with hydrazine in ethanol, it is acylated by a suitably activated carboxylic acid to produce an amide.
• Ring closure to an acylbenzoxazine can be achieved by treatment with formaldehyde, or a suitably substituted higher aldehyde to give stuctures of the type shown below:
• each R 1 and R 2 is as defined above and in addition may be an aromatic carbocyclic, aromatic heterocychc, or benzyl group, any of which may have structurally diverse variable substituents.
• Another method for the preparation of the compounds of the present invention comprises contacting the benzyl amine with an activated acid that contains an incipient aldehyde or ketone in the form of an acetal or ketal or oxidizable alcohol.
• the aldehyde or ketone is generated and catalyzed by a strong acid in a solvent of low basicity to cyclyze with the amide nitrogen and the phenol to give rotationally restricted structures of the type shown below:
• each R 1 and R 2 is as defined above and in addition may be an aromatic carbocyclic, aromatic heterocychc, or benzyl group, any of which may have structurally diverse variable substituents.
• the above-described compounds can be incorporated into a variety of formulations (e.g., capsule, tablet, timed-release capsule, syrup, suppository, injectable form, transdermal patch, etc.), preferably in combination with a pharmaceutically acceptable carrier, excipient or additive, for administration to a subject.
• various modes of delivery e.g., oral, buccal, rectal, parenteral, intraperitoneal, cutaneous, etc.
• Dose levels employed can vary widely, and can readily be determined by those of ordinary skill in the art. Typically, amounts in the milligram up to decigram quantities are employed. Oral administration (one to four times daily) is clearly preferred. Because of the unexpectedly favorable bioavailability and stability of compounds according to the present invention may be given orally as few as twice or even once, daily.
• Subjects contemplated for treatment with the invention compounds include humans, domesticated animals, laboratory animals, and the like.
• invention compounds can be used, for example, as a research tool for studying the biophysical and biochemical properties of the AMPA receptor and the consequences of selectively enhancing excitatory transmission on the operation of neuronal circuitry. Because invention compounds reach central synapses, they will allow for testing of the behavioral effects of enhancing AMPA receptor currents.
• Metabolically stable compounds which are positive modulators of AMPA currents have many potential applications in humans. For example, increasing the strength of excitatory synapses could compensate for losses of synapses or receptors associated with aging and brain disease (e.g., Alzheimer's). Enhancing AMPA receptors could cause more rapid processing by multisynaptic circuitries found in higher brain regions and thus could produce an increase in perceptual-motor and cognitive performance. As another example, because increasing AMPA receptor-mediated responses facilitates synaptic changes of the type believed to encode memory, metabolically stable AMPA modulators are expected to be functional as memory enhancers.
• Additional applications contemplated for the compounds of the present invention include improving the performance of subjects with sensory-motor problems dependent upon brain networks utilizing AMPA receptors; improving the performance of subjects impaired in cognitive tasks dependent upon brain networks utilizing AMPA receptors; improving the performance of subjects with memory deficiencies; and the like, as previously described.
• compositions of the present invention include correcting suboptimal system level communication between and among brain regions responsible for behaviors associated with psychiatric disorders, such as schizophrenia.
• invention compounds, in suitable formulations can be employed for decreasing the amount of time needed to learn a cognitive, motor or perceptual task.
• invention compounds, in suitable formulations can be employed for increasing the time for which cognitive, motor or perceptual tasks are retained.
• invention compounds, in suitable formulations can be employed for decreasing the quantity and/or severity of errors made in recalling a cognitive, motor or perceptual task.
• Such treatment may prove especially advantageous in individuals who have suffered injury to the nervous system, or who have endured disease of the nervous system, especially injury or disease which affects the number of AMPA receptors in the nervous system.
• Invention compounds are administered to the affected individual, and thereafter, the individual is presented with a cognitive, motor or perceptual task.
• compounds according to the present invention may be administered to a patient or a subject in need of therapy an effective amount of the compound.
• p-Toluenesulfonic acid monohydrate (3.61 g, 19.0 mmol) was dried by azeotropic distillation in a chloroform solution (100 mL). The remaining solution (50 mL) was cooled, 9.14 g (66.2 mmol) sesamol, 10.01 g (57 mmol) N-(hydroxymethyl)- phthalimide, and 100 mL chloroform were added, and the resulting green solution was refluxed overnight. The black reaction mixture was cooled to ambient, diluted to 500 mL with chloroform, and washed three times with saturated sodium bicarbonate.
• N-(2-Hydroxy-4,5-methylenedioxybenzyl)phthalimide (2.0 g; 6.7 mmol) was dissolved in 20 mL tetrahydrofuran (THF) under argon.
• aqueous phase was further extracted with dichloromethane (three times) and the pooled organic layers were combined and washed with 10% sodium hydroxide (three times) and with a saturated brine solution before being dried over sodium sulfate. Evaporation of the solvent and dissolution of the resulting brown liquid in ethyl ether gave crystals, which were collected by filtration and washed with ethyl ether/petroleum ether (1:1).
• N-(2-Ethoxymethoxy-4,5-methylenedioxybenzyl)phthalimide (1.70 g, 4.77 mmol) was treated with 0.5 mL (16 mmol) hydrazine in 90 mL refluxing ethanol for three hr.
• the reaction mixture was cooled and the phthalhydrazide was removed by filtration and washed three times with ethyl ether.
• the organic solutions were combined and evaporated to dryness on a rotary evaporator to yield a residue, which was taken up in dichloromethane.
• the organic solution was washed three times with 10%o sodium hydroxide and the combined aqueous solutions were back-extracted with dichloromethane two times.
• the amide/acetal (1.20 g, 3.12 mmol) from above was combined with 4 mL 2-propanol and 200 ⁇ L cone.
• the residue resulting from evaporation of the solvents was partitioned between water and dichloromethane.
• the aqueous layer was extracted with dichloromethane three times and the pooled organic fractions were washed twice with 10%) HC1, three times with 10%> sodium hydroxide, and once with brine prior to being dried over sodium sulfate.
• N-(hydroxymethyl)phthalimide (97.46 g, 42.1 mmol), 3,4- ethylenedioxyphenol (96.4 g, 42.1 mmol), and p-toluenesulfonic acid monohydrate (0.87 g, 4.6 mmol) were dissolved in 80 mL chloroform and the mixture was refluxed for three days under a Dean-Stark trap with occasional removal of water.
• the brown solution was filtered through a silica plug, the silica plug was washed with chloroform, and the combined organic solutions were evaporated to yield a yellow solid that was purified by flash chromatography with dichloromethane as eluent.
• the intermediate was obtained as a yellow solid (5.8 g) composed of a mixture of isomers, which was used without further purification.
• N-(2-ethoxymethoxy-4,5-ethylenedioxybenzyl)phthalimide (625 mg, 1.69 mmol) was mixed with 0.2 mL (6.4 mmol) hydrazine in 30 mL ethanol and refluxed for three hr. The reaction mixture was cooled, 30 mL ethyl ether was added to the mixture, and a white precipitate was removed by filtration. The filter cake was washed three times with diethyl ether and the combined organic solutions were evaporated to yield a residue that was partitioned between ethyl ether and 10% sodium hydroxide.
• 4,4-Diethoxybutyric acid (270 mg, 1.53 mmol) was activated by addition to a solution of 213 mg (1.31 mmol) of carbonyl diimidazole in 5 mL dichloromethane. The solution was stirred for 30 min, after which a solution of 347 mg (1.45 mmol) of 2- ethoxymethoxy-4,5-ethylenedioxybenzylamine in 1 mL dichloromethane was added and allowed to stand over night. The solution was washed with phosphate buffer (0.1 M, pH 6.8) three times and once with brine before being dried over sodium sulfate. The solution was filtered through a small plug of silica gel and evaporated to yield 436 mg (84%> crude) of an oil. IR: 3293 and 1644 cm "1 .
• the intermediate acid was added to a solution of 1.09 g (6.17 mmol) of carbonyl diimidazole in 20 mL of methylene dichloride. After 24 hr a white milky suspension was observed. A TLC analysis suggested some starting material remained and therefore an additional 474 mg CDI was added to the suspension. No further reaction was observed and the white solid was isolated by filtration and washed with dichloromethane. UV and IR spectra indicate that this intermediate (310 mg) is the acyl imidazole and therefore it was suspended in 10 mL dichloromethane and treated with 105 mg triethylamine for 4 days, at which time the reaction solution was homogeneous.
• invention compounds can be tested in vitro with slices of rat hippocampus according to the following procedure.
• Excitatory responses are measured in hippocampal slices, which are maintained in a recording chamber continuously perfused with artificial cerebrospinal fluid (ACSF).
• ACSF cerebrospinal fluid
• the perfusion medium is switched to one containing various concentrations of the test compounds.
• Responses collected immediately before and at the end of drug perfusion were superimposed in order to calculate both the percent increase in EPSP amplitude and percent increase in the width of the response at one-half the peak height (half- width).
• the hippocampus was removed from anesthetized, 2 month old Sprague-Dawley rats and in vitro slices (400 micrometers thick) were prepared and maintained in an interface chamber at 35 °C using conventional techniques [see, for example, Dunwiddie and Lynch, J. Physiol 276: 353-367 (1978)].
• the chamber was constantly perfused at 0.5 mL/min with ACSF containing (in mM): NaCl 124, KCl 3, KH2PO4 1.25, MgSO 4 2.5, CaCl 2 3.4, NaHCO3 26, glucose 10 and
• L-ascorbate 2 A bipolar nichrome stimulating electrode was positioned in the dendritic layer (stratum radiatum) of the hippocampal subfield CA1 close to the border of subfield CA3.
• the intensity of the stimulation current was adjusted to produce half-maximal EPSPs (typically about 1.5 - 2.0 mV). Paired stimulation pulses were given every 40 sec with an interpulse interval of 200 msec (see below).
• the field EPSPs of the second response were digitized and analyzed to determine amplitude, half- width, and response area. If the responses were stable for 15-30 minutes (baseline), test compounds were added to the perfusion lines for a period of about 15 minutes. The perfusion was then changed back to regular ACSF.
• Paired-pulse stimulation was used since stimulation of the SC fibers, in part, activates intemeurons which generate an inhibitory postsynaptic potential (EPSP) in the pyramidal cells of CA1.
• EBP inhibitory postsynaptic potential
• This feed forward IPSP typically sets in after the EPSP reaches its peak. It accelerates the repolarization and shortens the decay phase of the EPSP, and thus could partially mask the effects of the test compounds.
• One of the relevant features of the feed-forward IPSP is that it can not be reactivated for several hundred milliseconds following a stimulation pulse. This phenomenon can be employed to advantage to eliminate IPSP by delivering paired pulses separated by 200 milliseconds and using the second ("primed") response for data analysis.
• the field EPSP recorded in field CA1 after stimulation of CA3 axons is known to be mediated by AMPA receptors: the receptors are present in the synapses [Kessler et al, Brain Res. 560: 337-341 (1991)] and drugs that selectively block the receptor selectively block the field EPSP [Muller et al, Science, supra].
• Aniracetam increases the mean open time of the AMPA receptor channel and as expected from this increases the amplitude of the synaptic current and prolongs its duration [Tang et al. Science, supra].
• Invention compounds were assayed in the physiological test system described above for the generation of data presented in Table 1 below.
• a compound that lacks the rigidity of the benzoxazines of the present invention is also listed as the fifth entry. This serves as a comparison that illustrates the significant increase in activity derived by eliminating the two degrees of rotational freedom inherent in the nonrigid benzyl pyrrolidinone (compare 20%) increase in response at 300 ⁇ M of compound 1 to 20%> at 2 mM for the benzyl pyrrolidinone).
• the first two data columns of Table 1 show the half-life for plasma clearance (58 min) and the bioavailability (100%>) in the rat for the compound of Example 1. These data can be compared with those of the corresponding benzamide (Example 1 of U.S. patent no. 5,736,543, issued April 7, 1998), which exhibits a half-life and bioavailability of 31 min and 35%>, respectively.
• the third data column reports the magnitude of the increase in the amplitude of the EPSP at the lowest concentrations that produced a significant increase. The characteristic of a compound to produce an increase in the EPSP response has been a reliable predictor of the ability to improve memory in the 8-arm radial maze task.
• the last column of Table 1 describes the threshold dose for the most potent compound for enhancing memory in rats that were tested in a learning paradigm using an 8-arm radial maze as described in Staubli et al, PNAS 91 :11158-1162 (1994).

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